Abstract: A laser pattern generator for making a printed circuit board master image has its control data divided into image components according to whether a component is a simple figure such as a trace 32 that readily lends itself to conventional data compression coding or a more complex pattern 35 that is less readily coded. Data describing the complex patterns are prestored in a data library 358. Scan line elements of traces and patterns are independently assembled in separate work buffers 366-372. Data in the separate work buffers are then combined, either additively or subtractively, for assembly in a line assembly buffer 374 from which a data stream is derived for modulation of the laser 10. Additively combining data from the work buffers allows one image component to be electronically overlaid upon another, whereas subtractively combining data from the work buffers enables the pattern defined by subtractive data to be removed from another pattern.